A process for producing metal filaments directly from molten metal can be used for producing cheap metal filaments. Further, if the resulting metal filaments have an amorphous structure, they have a number of excellent chemical, electrical, and physical characteristics, and they have good applicability in many fields, such as electric and electronic parts, materials for reinforcement and fiber materials, etc. Particularly in the case of amorphous alloys, it is possible to emphasize the above described characteristics as compared with the prior crystalline alloys or crystalline metals, when a suitable alloy composition is selected. Particularly, from the viewpoint of corrosion resistance, stiffness and high magnetic permeability, it has been desired to develop new materials having desirable characteristics which have not been known heretofore. Amorphous metals have been broadly described already in Nippon Kinzoku Gakkai Kaiho, No. 3 Vol. 15 (1976); Science No. 8, 1978; Proceedings of the 2nd International Conference, edited by N. J. Grant and B. C. Giessen, Vol. II, Elsenier Sequoia S.A., Lausanne 1976; etc. Concerning amorphous metals having such desired excellent characteristics, it has been highly desired to produce high quality filaments having a round cross-section by a simple melt spinning process.
Heretofore, the production of amorphous metal filaments having a round cross-section by spinning molten metal directly into a cooling liquid to solidify the alloy filament has been limited to the case of alloys having a critical cooling rate of about 10.sup.3 .degree. C./second, such as Pd.sub.77.5 -Cu.sub.6 -Si.sub.16.5 alloy (numerals represent atomic %) (Scripta Metallurgia, Vol. 13, 1979, pages 463-467). The difficulty of formation of the amorphous alloy highly depends upon the kind and the composition of metals. It has been believed that amorphous metal is difficult to produce from Fe, Ni, and Co alloys, which would be particularly useful as practical materials for a number of uses, because they have a critical cooling rate in the range of about 10.sup.5 -10.sup.6 .degree. C./second, and the cooling rate thereof in a cooling liquid is low. Thus, therefore, in order to produce amorphous Fe, Ni, and Co alloys, a gun process, a piston-umbel process, a roll quenching process, a centrifugal quenching process, and a plasma-jet process, etc., which have high cooling rates, have been used. However, according to the above described processes, excepting the roll quenching process and the centrifugal quenching process, only plates having an unsettled shape can be obtained, i.e., thin pieces having no a definite shape such as a wire and a ribbon and a reproducibility in the production thereof cannot be obtained. In the roll quenching process and the centrifugal quenching process, only ribbon-shaped products having a fixed shape are obtained. Accordingly, such products can be used for only limited specific purposes because of having a flat shape. Processes for producing ribbon-shaped amorphous metal filaments have been described in the above described documents concerning amorphous alloys, as well as in Japanese Patent Application (OPI) Nos. 91014/74 (U.S. Pat. No. 3,856,513), 125228/78, 125229/78, 88219/77, 101203/75, 4017/76, 109221/76 (DT 2606581, FR 2301605), 12719/78, 12720/78, 133826/77 (DT 2719710, FR 2350159) and 88220/77 (The term "OPI" as used herein refers to a "published unexamined Japanese patent application".), and Japanese Patent Publication No. 50727/77, etc. Since these prior processes for producing amorphous metal filaments are based on a principle of jetting molten metal onto the surface of a quenching object, it has been unavoidable to flatten on the contacting surface and, consequently, it has been impossible to obtain filaments having a round cross-section. An attempt of producing filaments having a round cross-section by jetting molten metal to a roll surface having round cavities has been made, but the success in production has been very limited because the molten metal can not be perfectly jetted into the very fine cavities.
On the other hand, a number of processes have been developed in order to obtain metal filaments having a round cross-section directly from molten metal. For instance, there is a process similar to the so-called melt spinning process for producing synthetic fibers in a mass production, wherein a very unstable metal stream having a low viscosity is solidified by cooling while maintaining a continuous stream. For example, in Japanese Patent Publication 24013/70, a process has been proposed which comprises spinning into a gas atmosphere capable of reacting with metal to form an oxide or nitride film on the molten filament surface, as a stabilization means for solidifying with cooling. However, when this process is examined in detail, it is found to be very difficult to stabilize the molten metal by mere formation of such a film to the same degree as exists in the solid state. Moreover, this process is useful only for specific metals which form an oxide or nitride film.
Further, Japanese Patent Publication No. 25374/69 has disclosed a very useful means for cooling molten metal wherein fusing agent particles are sprayed to achieve a state of suspension in an inert gas in an ionizing zone by corona discharging, and the molten metal is cooled to solidify it by utilizing the latent heat of the fusing agent. With respect to similar cooling processes, processes which comprise spinning molten metal in foams or air bubbles to solidify by cooling have been proposed in, for example, Japanese Patent Applications (OPI) Nos. 56560/73 and 71359/73. These processes, however, have a low cooling rate and chenmical or electrostatic stabilization of the spinning stream is insufficient.
As another process, there is a composite spinning process for metal which utilizes spinnability of glass described in Kasen Geppo, No. 7, 1974, page 61. This composite spinning process is, however, effective for only the case of a specific combination concerning melt viscosity of glass and melting temperature of metal, and it can not be used for all metals. In addition, structures of the melting part and the spinning nozzle part are complicated, and a high accuracy is required because it involves composite spinning. Moreover, in the case of using these as metal filaments, it is necessary to remove the outer glass film, by which the cost of production becomes very high. Accordingly, this composite spinning process has many problems limiting industrial practice thereof.
Further, a process for producing metal filaments which comprises jetting spun molten metal in a cooling liquid flowing in parallel to the direction of jetting has been proposed as is shown in Japanese Patent Application (OPI) No. 1335820/74. However, in this process, since the spun molten metal and the cooling liquid run at the same rate as parallel streams, high cooling ability is insufficient. Particularly, the cooling liquid and the liquid level thereof are difficult to maintain stably, because of collision with the spun molten metal, boiling of the cooling medium, and convection currents, and consequently high quality amorphous metal filaments having a round cross-section can not be obtained by this process. Moreover, it is industrially difficult to directly continuously wind the solidified filaments.
Further, a process for producing continuous fine filaments of lead having a round cross-section which comprises putting water in a revolving drum to form a water membrane on the inner wall of the drum by centrifugal force, and jetting molten lead in the water membrane has been reported in 1978 in Nippon Kinzoku Gakkai, autumn convention, (83rd, at Toyama), lecture manuscript No. 331. However, this process can be adopted only for metals having good spinnability, such as lead, and it is impossible to form continuous fine filaments of amorphous alloy under the conditions that the jetting rate is higher than revolving rate of the drum which is the essential condition for practicing the process. In addition, the fine filaments of lead resulting in this process can not be practically used because they are not amorphous, the degree of roundness is inferior, and the size of the cross sectional area in the longitudinal direction is not uniform.
Moreover, amorphous metal wires of alloy consisting of Fe.sub.38 Ni.sub.39 P.sub.14 B.sub.6 Al.sub.3 (numerals are % by weight; Fe is 28 atomic %) have been described in Japanese Patent Application (OPI) No. 135820/74. However, these amorphous metal wires are expensive because of having the high Ni content.